This invention relates to telephone supervisory control circuits and more particularly to ring controlled circuits.
Numerous circuits are known in the prior art for generating a ring voltage and a telephone circuit. The U.S. Pat. No. 4,239,935 issued to Bosik et al. discloses a ring generator which uses trapezoidal shaped ringing signals to reduce cross-talk and interference. Current limiting is provided only for that part of the circuit connected to the subscriber loop. Zener diodes are used to protect against voltage spikes due to lightning. U.S. Pat. No. 4,220,826 issued to Kiss discloses a ringing generator which is self-adjusting as to load current demands. It provides a high-efficiency generator with constant output signal wave form under a variety of load current levels. A feedback arrangement is used whereby the output signal at the ringing end is fed back to a comparator which compares the output signal with an oscillator-produced sine wave signal of ringing frequency. This comparison provides an error signal which is used to modulate the high frequency signal on a pulse with modulator, so as to change the duty cycle of the modulated signal thus, changing the relative energy contained in the signal.
U.S. Pat. No. 4,239,941 issued to Gauthier et al. discloses a single telephone ringing generator that can ring a plurality of connected ringers, each having a different frequency ring. By means of a clock counters in a sweep frequency oscillator, 32 different frequencies are generated. The sweep frequency signal is then current amplified and fed to a frequency programmable filter which wave shapes the signal into a sinusoidal signal. Then, the sinusoidal signal is amplified to ringing voltage level.
A number of problems have existed with prior art circuits. Some of the circuits are designed for ring-trip detection, but are not related to a ringing generator. The prior art circuits are either not adjustable, have no output regulation neither voltage nor current, or are expensive to manufacture.
The present invention overcomes these problems in the prior art and provides a novel sine wave ring generator.